The antifungal effect of gaseous citral on various fungi by the modified gas method was investigated. The 22 spp. of fungi used in this experiment are often observed in stored products and some are pathogenic to men and animals. The concentrations of citral hexane solutions were 1,5, 10 and 20 mg/ ml and 0.05 ml impregnated in paper discs. Cultures were incubated at 28.degree. C and radial growth was measured every 24 h for 4 or 5 days. The growth inhibitory rate of citral to various fungi was calculated from the square measure of the colony after 72 h of incubation. In Trichoderma sp. the inhibitory activity of citral at each concentration was observed after 48 h incubation, but after 72 h only the 20 mg/ml of citral hexane solution inhibited the radial growth of fungi compared with that of control. Rhizopus nigricans, which grew most rapidly of the 22 spp. of fungi, the antifungal effect of citral was observed after 24 h incubation, but not observed at all after 48 h. The mycelium of that fungi expanded and covered all media even with 20 mg/ml of citral. The gaseous citral has an antifungal effect on all 22 spp. of fungi investigated. In the environment of the grain mites, citral released by the mite inhibits the growth of fungi and is indispensable to the survival of mites.